This invention relates generally to antenna structures, and more specifically to a planar inverted F antenna (PIFA) that is capable of being tuned via a variable grounding point.
A PIFA type antenna is utilized in many cellular telephones. However, the number, and configurations, of cellular telephones have increased significantly over the last several years. Currently, embedded PIFA design antennas are custom tuned for each specific cellular telephone style or platform. As such, a new and custom PIFA design is created, and then fabricated, for each new telephone type. Each antenna design typically contemplates a fixed grounding point and a fixed antenna feed point within the telephone.
A PIFA with more than one grounding connection is known. However, operation of this PIFA contemplates the switching of various impedances between the radiating element and the grounding plane. Addition of impedances and switches tend to act as transmission lines at the frequencies of operation. In addition, the number of switches and impedances in these antennas are limited as each adds one or more of size and cost to the product incorporating the antenna. As such, a truly variable grounding point antenna, which does not necessitate utilization of switches and impedances is needed.